Hip prosthesis with monoblock ceramic acetabular cup

ABSTRACT

An improved hip prosthesis includes an acetabular cup bearing component constructed from a relatively hard and high strength ceramic material for articulation with a ball-shaped femoral head component which may be constructed from a compatible ceramic or metal material. In one form, the acetabular cup further includes a ceramic porous bone ingrowth surface adhered thereto for secure ingrowth attachment to natural patient bone.

This application is a continuation-in-part of copending U.S. Ser. No.10/987,415, filed Nov. 12, 2004, which is a division of U.S. Ser. No.10/171,376, filed Jun. 13, 2002, which in turn claims the benefit ofU.S. Provisional Application. 60/289,669, filed Jun. 14, 2001.

This application is also a continuation-in-part of copending U.S. Ser.No. 11/040,477, filed Jan. 20, 2005, which is a continuation-in-part ofU.S. Ser. No. 10/137,106, filed Apr. 30, 2002, now U.S. Pat. No.6,846,327, issued Jan. 25, 2005, which in turn claims the benefit ofU.S. Provisional Application 60/287,824, filed May 1, 2001.

BACKGROUND OF THE INVENTION

This invention relates generally to improvements in hip jointprostheses, particularly with respect to an improved acetabular cupbearing component constructed from a relatively hard and relatively highstrength ceramic material. The ceramic acetabular cup is designed fordirect articulation against an associated femoral head component formedfrom a compatible ceramic or metal material, with minimal component wearto achieve substantially optimal prosthesis service life. The presentinvention thus permits elimination of a conventional polymer-basedbearing insert thereby also eliminating undesirable wear debrisassociated therewith.

Hip prostheses generally comprise a femoral component adapted forfixation to an upper end of the patient's femur, and defining agenerally ball-shaped head for articulation relative to an acetabularcup component which is adapted in turn for seated fixation within thepatient's acetabulum. A polymer-based bearing insert such as acup-shaped component formed from a typically high density or highmolecular weight polyethylene (PE) or the like is normally fittedbetween the femoral head and the acetabular cup to accommodate smoothand relatively low-wear articulation between these components.

However, clinical studies have shown that significant wear debris can begenerated and released by the polymeric bearing insert over a period oftime, and further that a principle contributing factor to implantfailure is osteolysis attributable at least in part to the presence ofsuch polymer-based wear debris. More particularly, such studies haveshown that PE wear debris released into peri-implant tissues appears toelicit a deleterious biological reaction, incorporating foreign bodygiant cell and macrophage cell responses leading to undesirable boneresorption, with eventual loosening and failure of the prostheticimplant. As a result, alternative prosthesis constructions have proposedimprovements in and to the polymer-based bearing insert, such as the useof heavily cross-linked polyethylene materials. Other alternativeprostheses have been proposed using rigid-on-rigid components, such asceramic-on-ceramic or metal-on-metal, thereby eliminating thepolymer-based bearing insert and wear debris associated therewith.

In general, ceramic hip prosthesis components have shown promise for usein a ceramic-on-ceramic or alternately in a ceramic-on-metalarticulating interface, thereby completely eliminating the polymer-basedbearing insert. Such prosthesis constructions, when formed with a goodsurface finish and conformal surface geometry, have demonstrated arelatively low coefficient of friction and resultant substantialreduction in component wear in comparison with ceramic-polymer ormetal-polymer articulatory interfaces. However, the major limitation onthe use of ceramic components particularly such as alumina-based ceramicmaterials has been an unacceptably high rate of brittle fractureoccurring within a post-surgical follow-up period ranging from a fewmonths to several years. In this regard, ceramic materials generallyexhibit relatively low toughness and are thus prone to brittle fracture.

U.S. Publication US 2003/0153984 discloses an improved ceramic materialfor use in joint prostheses, such as hip prostheses, wherein aceramic-on-ceramic or a ceramic-on-metal articulatory interface isdefined. The improved ceramic material comprises a doped silicon nitride(S₃N₄) having relatively high hardness, tensile strength, elasticmodulus, lubricity, and fracture toughness. Specifically, the improveddoped silicon nitride ceramic has a flexural strength greater than about700 Mega-Pascal (MPa) and a fracture toughness greater than about 7Mega-Pascal root meter (MPam^(0.5)). This high strength and hightoughness doped silicon nitride ceramic achieves ultra-low wear over anextended service life, with dramatically reduced risk of brittlefracture.

In addition, U.S. Pat. No. 6,846,327 discloses improved ceramicmaterials for bone graft applications, wherein the ceramic material isdesigned to mimic structural characteristics of natural patient bone byincluding first and second regions of comparatively lower and higherporosity to respectively mimic natural cortical and cancellous bonestructures. The preferred ceramic materials disclosed exhibit a flexuralstrength greater than about 500 Mega-Pascal (MPa) and a fracturetoughness greater than about 5 Mega-Pascal root meter (MPam^(0.5)). Inuse, the relatively low porosity region of the ceramic material provideshigh structural strength and integrity, whereas the higher porosityregion is suitable for bone ingrowth to achieve secure and stableimplant affixation.

The present invention comprises an improved hip joint prosthesisparticularly wherein the acetabular cup component thereof is constructedfrom an improved high strength and high toughness ceramic material asdisclosed, e.g., in U.S. Publi. US 2003/0153984 and/or U.S. Pat. No.6,846,327.

SUMMARY OF THE INVENTION

In accordance with the invention, an improved hip prosthesis includes anacetabular cup bearing component constructed from a relatively highstrength and high toughness ceramic material for ultra-low weararticulation with a ball-shaped femoral head component which may beconstructed from a compatible ceramic or metal material. In one form,the acetabular cup further includes a ceramic porous bone ingrowthsurface for secure ingrowth affixation to natural patient bone.

In one preferred form of the invention, a unipolar hip joint prosthesisincludes the ceramic acetabular cup having a generally shell-shaped orcup-shaped geometry defining a relatively low porosity substrate incombination with a comparatively higher porosity bone ingrowth surface.The low porosity ceramic substrate defines a downwardly open,part-spherical cavity for receiving and articulating with a ball-shapedfemoral head of a femoral component, wherein the femoral head may beconstructed from a compatible and preferably identical high strength andhigh toughness ceramic material, or alternately from a compatible metalmaterial such as biocompatible cobalt chrome alloy or the like. Thehigher porosity ceramic bone ingrowth surface extends over an uppersurface of the acetabular cup for suitable seated contact within aprepared patient acetabulum, for secure affixation thereto by boneingrowth.

The ceramic acetabular cup of the hip prosthesis may incorporate a lowerfree circumferential edge or margin defined by a pair of shallow reliefsegments formed at diametrically opposed positions corresponding withthe flexion/extension plane. The inclusion of these relief segmentsbeneficially provides the patient with an enhanced range-of-motion(ROM).

The relief segments may be in the form of cutouts or recesses.Alternatively, the acetabular cup may employ a single cutout or relief,or multiple cutouts or reliefs may be used. Further the cutouts orreliefs can be symmetrically configured or asymmetrically configured.For example, the cutouts or reliefs can be diametrically oppositelydisposed, spaced adjacent to each other, or spaced in othercircumferential orientations.

Other features and advantages of the present invention will becomeapparent from. the following more detailed description, taken inconjunction with the accompanying drawings, which illustrate, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a fragmented perspective view illustrating an exemplary hipprosthesis in an installed position affixed to a patient's femur andacetabulum;

FIG. 2 is an enlarged and exploded perspective view showing componentsof an improved hip prosthesis embodying the novel features of theinvention;

FIG. 3 is a further enlarged and fragmented sectional view depictingdetails of an acetabular cup used in the hip prosthesis of FIG. 2;

FIG. 4 is an exploded perspective view showing one alternative preferredform of a hip prosthesis;

FIG. 5 is a perspective view illustrating an alternative preferredgeometry for an acetabular cup component for use in the invention;

FIG. 6 is a side elevation view of the acetabular cup of FIG. 5; and

FIG. 7 is a sectional view taken generally on the line 7-7 of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the exemplary drawings, an improved hip prosthesis referredto generally in one preferred form by the reference numeral 10 in FIGS.2-3 includes an acetabular cup 12 constructed from a relatively hard andhigh strength ceramic material which may also incorporate a relativelyporous ceramic bone ingrowth surface 14 for secure affixation to patientbone. The cup 12 is designed for articulation with other prosthesiscomponents such as a ball-shaped femoral head component 16 which may beconstructed from a hard and high strength material such as a compatibleand preferably identical ceramic material, or a biocompatible metalmaterial (FIG. 4). The resultant ceramic-on-ceramic or ceramic-on-metalarticulatory interface beneficially exhibits ultra-low wear over anextended service life, while additionally permitting elimination oftraditional polymer-based bearing inserts and wear debris problemsassociated therewith.

FIG. 1 illustrates a traditional hip prosthesis construction forrepairing or replacing the natural anatomical ball-and-socket human hipjoint. More specifically, FIG. 1 shows an acetabular cup 12 seatedand/or affixed within the patient's natural acetabulum or socket 17, incombination with a femoral component 18 including an elongated stem 20(FIG. 2) seated within a resected upper end of the patient's femur bone22, an upwardly protruding femoral neck 24, and the ball-shaped femoralhead 16 mounted or otherwise formed on an upper end of the neck 24.Accordingly, a generally cup-shaped bearing insert 26 formed typicallyfrom a polymer-based material such as a high density or high molecularweight polyethylene (PE) or the like is normally fitted between theacetabular cup 12 and the femoral head 16 to accommodate smootharticulation between these components. However, as previously notedherein, premature prosthesis failure has been attributed to thegeneration and accumulation of polymer-based wear debris associated withthe bearing insert 26. A further drawback to the use of polymer-basedinserts is the higher thickness of the construct, restricting itsapplication to larger bone patients capable of receiving the largersizes, and thus preventing the use of larger diameter heads in smallerbone patients.

Accordingly, the present invention is particularly directed to theprovision of an improved hip joint prosthesis 10 constructed in any oneof a plurality of alternative preferred forms, to include improvedimplantable and biocompatible materials designed for achieving ultra-lowwear as a consequence of component articulation over an extended servicelife or duty cycle, using a ceramic-on-ceramic or a ceramic-on-metalarticulatory interface, and omitting use of the traditionalpolymer-based bearing insert.

The present invention is also particularly directed to the provision ofan improved hip joint prosthesis 10 constructed in any one of aplurality of alternative preferred forms, to include improvedimplantable and biocompatible materials designed for achieving a thinneroverall acetabular cup diameter, and as a consequence, providing theability to use larger diameter heads on smaller bone patients thanotherwise possible, using a ceramic-on-ceramic or a ceramic-on-metalarticulatory interface, and omitting the use of traditionalpolymer-based bearing inserts.

FIGS. 2-3 illustrate the improved hip prosthesis 10 in one preferredunipolar form. As shown, the acetabular cup 12 has a generallycup-shaped or shell-shaped geometry defining a downwardly openpart-spherical and substantially hemispherical cavity 28. Thisshell-shaped acetabular cup 12 has a size selected for substantiallyconformal seated reception into the generally matingly shaped acetabulumor socket 17 (FIG. 1) which may be surgically prepared as by removal ofaccumulated calcium deposits or other procedures known in the art.Importantly, in accordance with a primary aspect of the invention, theacetabular cup 12 is formed from a relatively high strength and hightoughness or high hardness ceramic material defining a part-sphericalsubstrate 30 lining the cavity 28 to define an articulation surface forreceiving and articulating against the ball-shaped femoral head 16.

More specifically, the preferred ceramic material used for constructingthe ceramic acetabular cup 12 of the present invention comprises a highflexural strength and high fracture toughness ceramic materialparticularly such as a doped silicon nitride (S₃N₄) having relativelyhigh hardness, tensile strength, elastic modulus, lubricity, andfracture toughness properties, as described in detail in U.S. Publi.2003/0153984 which is incorporated by reference herein. This dopedsilicon nitride ceramic material has a relatively high flexural strengthgreater than about 700 Mega-Pascal (MPa) and a relatively high fracturetoughness greater than about 7 Mega-Pascal root meter (MPam^(0.5)). Thishigh strength and high toughness doped silicon nitride ceramic achievesultra-low wear over an extended service life, with dramatically reducedrisk of brittle fracture.

In the preferred form as shown best in FIG. 3, this high strength andhigh toughness ceramic material is used to form the substrate 30 of theceramic acetabular cup 12. In this regard, the substrate 30 of theceramic cup 12 has a relatively low porosity, and thus exhibits highdensity and high structural integrity generally consistent with andgenerally mimicking the characteristics of natural cortical bone linedwith smooth lubricious articular cartilage. FIG. 3 further shows asurface coating or lining 14 formed on the part-spherical upwardlypresented surface or convex upper side of the cup 12, wherein thiscoating or lining exhibits a comparatively greater or higher porositythat is generally consistent With and generally mimics thecharacteristics of natural cancellous bone. As a result, this higherporosity surface coating or lining 14 provides an effective boneingrowth surface for achieving secure and stable bone ingrowthaffixation of the ceramic acetabular cup 12 within the patient'sacetabulum.

While persons skilled in the art will recognize and appreciate that thespecific material used for the bone ingrowth surface coating or lining14 may vary, a preferred porous material comprises a ceramic porousingrowth surface material. In this regard, U.S. Pat. No. 6,846,327 whichis incorporated by reference herein discloses a ceramic bone graftcomponent having relatively high flexural strength and relatively hightoughness properties yet defining first and second regions ofcomparatively lower and higher porosity to respectively mimic naturalcortical and cancellous bone structures. These regions of differentporosity may be unitarily constructed or otherwise integrated into acommon or monolithic ceramic component having a variable porositygradient. In a preferred form, the ceramic cup 12 has a porositygradient ranging from about 2% to about 80% by volume, with the higherporosity region having a porosity in the range of from about 30% toabout 80% by volume, and with overall pore sizes ranging from about 100microns to about 500 microns. In use, the relatively low porosity regionof the ceramic material provides a dense and hard structure with highstructural strength and integrity, whereas the higher porosity or lessdense region is suitable for bone ingrowth to achieve secure and stableimplant affixation.

U.S. Pat. No. 6,846,327 discloses a preferred alumina-zirconia ceramicmaterial having a zirconia composition of about 10% to about 20% byvolume, with either yttria stabilized zirconia (about 2.5 to about 5 mol% yttria in zirconia) or ceria stabilized zirconia (about 2.5 to about15 mol % ceria in zirconia) for the zirconia phase. The resultantceramic material exhibits a highly desirable combination of highflexural strength (greater than about 500 MPa) and high fracturetoughness (greater than about 5 MPam^(0.5)). Such alumina-zirconia basedceramic material may be employed in the present invention for theceramic acetabular cup 12, although the harder and tougher siliconnitride (S₃N₄) ceramic as described in U.S. Publi. 2003/0153984 ispreferred.

FIG. 3 shows the ceramic acetabular cup 12 to include the substrate 30formed from relatively low porosity ceramic material having the desiredhigh strength and high toughness properties, such as the doped siliconnitride (S₃N₄) material described in the above-referenced U.S. Publi.2003/1053984, wherein this low porosity ceramic material lines anddefines the concave part-spherical cavity 28. FIG. 3 further shows thecomparatively higher porosity bone ingrowth surface 14, formedpreferably from a higher porosity ceramic material as described in theabove-referenced U.S. Pat. No. 6,846,327, extending over a substantialarea of the convex upper side of the acetabular cup 12. As noted, thisbone ingrowth surface 14 may be formed integrally with or otherwiseapplied to the substrate 30.

The femoral head 16 is sized and shaped for articulatory receptionwithin the acetabular cup cavity 28. In a preferred form as viewed inFIG. 2, the femoral head 16 is constructed from a ceramic material thatis compatible with the ceramic cup material. In this regard, a preferredmaterial for the femoral head 16 comprises a matching or identical highstrength and high toughness ceramic material corresponding with theacetabular cup material, as disclosed in U.S. Publi. 2003/1053984.Alternately, as viewed in one preferred alternative unipolar embodimentof the invention depicted in FIG. 4, a modified femoral head 16′ may beconstructed from a biocompatible metal material, preferably such as acobalt chrome alloy as disclosed in the above-referenced 2003/1053984.

FIGS. 5-7 depict a modified ceramic acetabular cup 12′ which may beincorporated into any one of the foregoing embodiments of the inventionas shown in FIGS. 2-4 and previously described herein. In this regard,FIGS. 5-7 show the modified acetabular cup 12′ to include the relativelylow porosity substrate 30 defining the downwardly presentedpart-spherical cavity 28, in combination with the bone ingrowth coatingor surface 14 on the upwardly presented or convex side thereof. Personsskilled in the art will appreciate that the bone ingrowth coating orsurface may be omitted, as previously described herein. Importantly, thecircumferential free edge or margin 60 of the ceramic cup 12′incorporates a pair of smoothly contoured, shallow relief segments 62and 64 formed generally at diametrically opposed positions correspondingwith the flexion/extension plane during normal patient movements. Theinclusion of these shallow relief segments 62 and 64 beneficiallyprovides the hip prosthesis and thus the patient with an enhancedrange-of-motion (ROM).

A variety of further modifications and improvements in and to the hipprosthesis of the present invention will be apparent to persons skilledin the art. For example, it will be understood that the ceramicacetabular cup component as shown and described herein may be used forarticulatory engagement with the natural ball-shaped femoral head at theupper end of the patient's femur, or with an appropriately cappednatural femoral head, in lieu of a prosthetic femoral head. Accordingly,no limitation on the invention is intended by way of the foregoingdescription and accompanying drawings, except as set forth in theappended claims.

1. A hip joint prosthesis, comprising: a generally shell-shapedacetabular cup defining a convex upper side having a size and shapeadapted for seated engagement within a patient's natural acetabulum, anda lower side defining a downwardly open and generally part-sphericalcavity lined by an articulation surface having a size and shape forarticulatory reception of a matingly shaped femoral component; saidacetabular cup being formed from ceramic material having relatively higha relatively high flexural strength and a relatively high fracturetoughness for ultra-low wear upon post-implantation articulation withsaid matingly shaped femoral component.
 2. The hip joint prosthesis ofclaim 1 wherein said ceramic material has a relatively high flexuralstrength greater than about 500 Mega-Pascal (MPa) and a relatively highfracture toughness greater than about 5 Mega-Pascal root meter(MPam^(0.5)).
 3. The hip joint prosthesis of claim 1 wherein saidceramic material has a relatively high flexural strength greater thanabout 700 Mega-Pascal (MPa) and a relatively high fracture toughnessgreater than about 7 Mega-Pascal root meter (MPam^(0.5)).
 4. The hipjoint prosthesis of claim 3 wherein said ceramic material comprisesdoped silicon nitride.
 5. The hip joint prosthesis of claim 1 furtherincluding a bone ingrowth surface on said convex upper side of saidacetabular cup.
 6. The hip joint prosthesis of claim 1 wherein said boneingrowth surface comprises a ceramic bone ingrowth surface.
 7. The hipjoint prosthesis of claim 6 wherein said acetabular cup comprises aceramic material having a variable porosity gradient defining arelatively low porosity first region forming a substrate defining saidarticulation surface, and a comparatively higher porosity second regiondefining said ceramic bone ingrowth surface, said first and secondregions being integrally formed.
 8. The hip joint prosthesis of claim 7wherein said ceramic material has a porosity gradient ranging from about2% to about 80% by volume, with said higher porosity region having aporosity in the range of from about 30% to about 80% by volume.
 9. Thehip joint prosthesis of claim 8 wherein said ceramic material has poresformed therein with a pore size ranging from about 100 microns to about500 microns.
 10. The hip joint prosthesis of claim 1 wherein saidmatingly shaped femoral component comprises a ball-shaped femoral head.11. The hip joint prosthesis of claim 10 wherein said femoral head isformed from a ceramic material.
 12. The hip joint prosthesis of claim 10wherein said femoral head is formed from a ceramic materialsubstantially identical to the acetabular cup ceramic material.
 13. Thehip joint prosthesis of claim 10 wherein said femoral head is formedfrom a biocompatible metal.
 14. The hip joint prosthesis of claim 10further including a retainer for movably retaining said acetabular cupon said femoral head.
 15. A hip joint prosthesis, comprising: agenerally shell-shaped acetabular cup defining a downwardly open andgenerally part-spherical cavity lined by an articulation surface havinga size and shape for articulatory reception of a matingly shaped femoralcomponent; said articulation surface of said acetabular cup being formedfrom ceramic material having relatively high a relatively high flexuralstrength and a relatively high fracture toughness for ultra-low wearupon post-implantation articulation with said matingly shaped femoralcomponent; said acetabular cup further defining a convex upper sidehaving a porous bone ingrowth surface thereon and further defining asize and shape adapted for seated engagement within a patient's naturalacetabulum.
 16. The hip joint prosthesis of claim 15 wherein saidacetabular cup comprises a ceramic material having a variable porositygradient defining a relatively low porosity first region forming asubstrate defining said articulation surface, and a comparatively higherporosity second region defining said bone ingrowth surface, said firstand second regions being integrally formed.
 17. The hip joint prosthesisof claim 15 wherein said matingly shaped femoral component comprises aball-shaped femoral head.
 18. The hip joint prosthesis of claim 17wherein said femoral head is formed from a ceramic materialsubstantially identical to the acetabular cup ceramic material.
 19. Thehip joint prosthesis of claim 17 wherein said femoral head is formedfrom a biocompatible metal.
 20. A hip joint prosthesis, comprising: agenerally shell-shaped acetabular cup defining a convex upper side andhaving a size and shape adapted for seated engagement within a patient'snatural acetabulum, and a lower side defining a downwardly open andgenerally part-spherical cavity lined by an articulation surface havinga size and shape for articulatory reception of a matingly shaped femoralcomponent; said acetabular cup being formed from ceramic material havinga relatively high flexural strength and a relatively high fracturetoughness for ultra-low wear upon post-implantation with said matinglyshaped femoral component; and said acetabular cup having a rim with arecessed geometry for increase range of motion.
 21. The hip jointprosthesis of claim 20 wherein said rim includes multiple recessesformed therein for enhanced range of motion.
 22. The hip jointprosthesis of claim 20 wherein said rim includes a pair of generallydiametrically opposed recesses formed therein for enhanced range ofmotion.